The invention relates to a method or process for improving the sound signal as presented to the eardrum or tympanic membrane of a user.
Measurements and corrections of this kind are, at least in parts, known from the prior art.
Thus, German Publication DE 28 08 516 A1 discloses a hearing aid using, in addition to the receiver, a measurement microphone, preferably as a unitary device, to develop in the earcanal in front of the eardrum a corresponding signal which may be used for the compensation of linear and/or nonlinear distortions. The instantaneous values of the signal from the probe microphone are compared with the undistorted output signal of the preamplifier in a differential amplifier resulting in a correction voltage which is added to the input signal of the output amplifier, resulting in a corrected output signal from the receiver.
In the U.S. Pat. No. 4,596,902 a processor controlled hearing aid is disclosed using a feedback microphone located in the earcanal to develop a control signal representative of the spectrum of the actual sound pressure levels by frequency in front of the eardrum. A processor compares averages of the actual sound pressure levels in front of the eardrum with the desired levels for the overall output in accordance with a predetermined set of reference instructions stored in a memory, and thus, controls the channel amplifiers and an output amplifier to produce the desired sound pressure levels in the earcanal in front of the eardrum.
In DE 41 28 172, a hearing aid is disclosed with an input transducer, an output transducer and a microprocessor connected between the input and the output transducers for digital signal processing of the input transducer signal. The processor transferfunction of the digital signal processing is stored in an EEPROM. The hearing aid further comprises testing means for sensing the actual sound pressure levels in the earcanal. The hearing aid operates in two differently distinct modes, namely a hearing aid mode and a measuring mode. The actual operating mode may be selected by the user. In the measuring mode the microprocessor generates a sequence of different tones of stepwise ascending volumes, and the sensing means senses the resulting sound pressure levels in the earcanal. The measured levels are compared with predetermined stored levels and corrections to the stored parameters of the transmission characteristic representative of said levels are performed in response to the determined differences. Thus, corrections can not be performed in real time.
CH 678 692 A discloses a method and an apparatus for determining individual acoustical properties of a human ear wearing a hearing aid. The apparatus consists of an in-the-ear hearing aid with a microphone, an amplifier and a loudspeaker. The hearing aid further comprises a sensing microphone for sensing sound emitted by the loudspeaker for determination of the acoustical properties in-situ. In one embodiment, the loudspeaker is alternatingly operating as a loudspeaker and a microphone.
Thus, it is an object of the present invention to create or develop a new method or process of the kind referred to above by which such measurements and corrections could be executed almost in real time, and to use such a method to generate an error signal and use such an error signal for correcting or adjusting the sound signal as presented in front of the eardrum in real time, to facilitate adjustment of the sound signals in the earcanal dynamically to instantaneous variations in the conditions prevailing between the sound outlet in the earcanal and the eardrum.
This new method to measure and correct or adjust the sound signal presented to the eardrum by means of a hearing aid in the operational position, including at least one microphone, at least one digital processing system comprising at least one digital signal processor for transforming the incoming sound signal into a transformed signal in conformity with a desired transformation function, at least one receiver and a power supply, and having at least one sensing means for sensing the signal appearing in front of the eardrum, said method using a reference signal representative of a desired sound signal in front of the eardrum, is characterized by generating a reference signal in a reference signal processor, said reference signal being based on an output signal of at least one microphone and being representative of a desired signal in front of the eardrum, establishing a transfer function between the receiver and the output of the sensing means, correcting the process in said reference signal processor in conformity with said transfer function, sensing the sound signal in front of the eardrum and feeding said sensed signal back to an input of the signal processing system, comparing said sensed signal in a comparison means with the corrected reference signal and, in case there is a material difference between the sensed signal and the corrected reference signal, correcting said transformed signal into a corrected transformed signal for adjusting the signal in front of the eardrum to the desired sound signal.
It is particularly advantageous, if the entire operation is performed digitally, which would lead to large scale integration of most or almost all components of the system.
Further advantages of the invention will become apparent from the remaining claims and the description.